When blood vessels narrow, they help increase blood pressure. Thinking only about smooth muscle in the arms, you know that Select one: a. Acetylcholine increases calcium levels in arm smooth muscle b. Epinephrine increases calcium levels in arm smooth muscle c. Acetylcholine decreases calcium levels in arm smooth muscle d. Epinephrine decreases calcium levels in arm smooth muscle

The correct answer is: D. Epinephrine decreases calcium levels in arm smooth muscle.

Explanation:

Smooth muscle makes up an important part of the structure of blood vessels' walls. Its main function is to contract or relax when the body requires to do so, directly impacting blood pressure. When the smooth muscle in arteries contracts, blood pressure rises; and when the smooth muscle relaxes, blood pressure decreases.

For the smooth muscle to be able to contract, calcium needs to be present thanks to the stimulation of neurotransmitters.

When Epinephrine is released, it can interact with different types of receptors depending on the tissue or organ. In the majority of smooth muscle, epinephrine contacts alpha-1 adrenergic receptors and produces an effect of vasoconstriction (contraction of the blood vessel), BUT in the smooth muscle located in the blood vessels of skeletal muscles, like the one in the arms, epinephrine interacts with beta-2 adrenergic receptors and generates the opposite effect: it produces vasodilation - the relaxation of the smooth muscle.

In conclusion, when Epinephrine is released, it produces a decrease in the calcium levels in the arms smooth muscle.